Pushing and pulling with the upper extremities while standing: the effects of mild Alzheimer dementia and Parkinson's...

Eleven patients with mild dementia of Alzheimer type, 12 patients with mild to moderate Parkinson disease, and 27 control subjects of comparable age, education, and gender pushed or pulled on a rigid horizontal bar while maintaining stable erect stance. A target window (target force +/-10% maximum force) and a bar force cursor were displayed on a video screen, and subjects were asked to place the bar force cursor within the target window as quickly and as accurately as possible holding the target window for at least 1 sec. The target forces were 50% and 75% maximum force for each person, and three 4.0-sec push trials and three 4.0-sec pull trials were performed for each target force. Moments of force (torque), body motion, and extremity electromyography were measured with a computerized motion analysis system. The patients with Alzheimer's disease had only slightly lower Mini Mental State Examination (MMSE) scores (mean +/- standard deviation [SD] = 25.0 +/- 2.3) than the patients with Parkinson's disease (28.8 +/- 1.5) and control subjects (28.7 +/- 1.3). The patients with Alzheimer's disease had upper limb reaction times (0.827 +/- 0.399 sec) that were greater than those of the patients with Parkinson's disease (0.672 +/- 0.315 sec) and control subjects (0.606 +/- 0.263 sec). Furthermore, the patients with Alzheimer's disease achieved the designated target in only 46.2% of trials, which was comparable to the performance of the patients with Parkinson's disease (55.6%) but inferior to the control subjects (80.6%). Movement times did not differ significantly. The patients and control subjects initiated movement with comparable anticipatory postural activity in the lower limbs. The poor success rates of the patients with Alzheimer's disease and the patients with Parkinson's disease were attributable to inadequate visually guided adjustments in force after the initial movement began. This difficulty in making quick motor adjustments may be relevant to the tendency of patients with Alzheimer's disease to fall.